Burke said he did not anticipate any problems with projects or clients because of the transaction nor any significant antitrust issues. He noted required filings in just three countries, adding that the industry's top five firms have just 20% of the total market.

The firms are expected to integrate quickly. An already developed organization chart is "evidence" of that, said the source.

Burke would not say if the combined company might have a new name when the deal is completed.

While observers say URS has been more adept at integration, Burke emphasized the firms' "extensive integration experience." Koffel added that leadership has the "talent to conceive of and execute" a 95,000-person organization.

AECOM will elect two URS board members to its board and John M. Dionisio, AECOM executive chairman, will be the combined firms' chairman.

Randall Wotring, president of URS' federal business, will lead the combined firms' work in the federal sector, according to a source close to the transaction.

The transaction would link the industry's first and third-largest global engineers. AECOM ranks at No. 1 on ENR's list of the Top 500 Design Firms, with $7.2 billion in global revenue; URS ranks at No. 3, with $5.27 billion.

URS also ranks at No. 16 on ENR's list of the Top 400 Contractors, with $4 billion in global construction revenue. AECOM ranks at No. 6 on ENR's list of the Top Construction Management for Fee companies, with $912 million in 2013 revenue.

The companies said URS stockholders "will receive per-share consideration equal to $33.00 in cash and 0.734 shares of AECOM common stock for each URS share and will own 35% of the combined company when the deal is completed."

Both company boards have unanimously approved the agreement, the firms said, adding that the combined company would be located in Los Angeles, where AECOM has its corporate headquarters. It also will maintain "a key operational presence" in San Francisco, where URS is based, the firms noted.

AECOM, which will release third-quarter results on Aug. 5, said it "continues to target diluted earnings per share (EPS) in the lower end of its range of $2.50 to $2.60 for fiscal 2014, excluding transaction-related costs."

But it said backlog, which AECOM noted was $30 billion for the combined firms, remains at record levels.

URS had hired Citigroup and DBO Partners to contact potential buyers, according to a July 11 Reuters story that said some private equity firms had "passed" on the deal.

According to the transaction source, the private equity offer was not financially acceptable to URS nor did it offer any synergy.

AECOM was one of URS' cited competitors, along with Fluor Corp., Jacobs Engineering, CB&I and Tetra Tech, although Reuters did not say if any of the other firms had made offers.

Paul Zofnass, EFCG president, said, "To me, it was the obvious play. Here are two firms, each of [which] have been pursuing the same strategy for the past 25 years to become the biggest player" in the engineering sector. "What could make more sense than for them to ultimately merge with each other?" Zofnass asked.

He added that the deal could create opportunities for smaller and mid-size firms that "have made it part of their policy to hire away from the consolidators."

Added Zofnass, "This merger should make for good hunting."